Project description:Despite recent advances in the identification of lymphoid-restricted progenitors, the transcription factors essential for their generation remain to be identified. Here we describe an unexpected role for the myeloid oncogene Mef2c in multipotent progenitors (MPPs), where it is required for pan-lymphoid differentiation. Mef2c deficiency was associated with profound defects in B, T, NK cell and common lymphoid progenitor production and an enhanced myeloid output. Mef2c deficiency in MPPs leads to downregulation of several key lymphoid regulators and the upregulation of the myeloid factor C/EBPa. Our studies also show that Mef2c is a critical transcriptional target of PU.1 during lymphopoiesis. Thus, Mef2c is a crucial component of the transcriptional network that regulates lymphoid specification and cell fate choice in MPPs.
Project description:Myeloid-biased differentiation of multipotent hematopoietic stem and progenitor cells (HSPCs) occurs with aging or exhaustion. The molecular mechanism(s) responsible for this fate bias remain unclear. Here we report that linker histone regulates HSPC fate choice at the lymphoid versus myeloid bifurcation. Linker histones package nucleosomes and compact chromatin. HSPCs expressing a doxycycline (dox) inducible H1.0 transgene favor the lymphoid fate, display strengthened nucleosome organization and reduced chromatin accessibility at subsets of genomic regions. The genomic regions showing reduced chromatin accessibility host many known marker genes of myeloid biased HSCs. The transcription factor Hlf is located in one of the most differentially closed regions, whose chromatin accessibility and gene expression are reduced in H1.0high HSPCs. Failure to reduce Hlf expression in multipotential HSPCs abrogates the H1.0-endowed lymphoid potential. Furthermore, HSPCs display aspartyl protease dependent H1.0 decreases, especially in response to interferon alpha (IFNa). Aspartyl protease inhibitors preserve endogenous H1.0 levels and promote the lymphoid fate of wild type HSPCs. Thus, our work elucidates a molecular scenario how myeloid bias arises and uncovers a point of intervention for correcting myeloid skewed hematopoiesis.
Project description:Cellular binary fate decisions require the progeny to silence genes associated with the alternative fate. The major subsets of alpha:beta T cells have been extensively studied as a model system for fate decisions. While the transcription factor RUNX3 is required for the initiation of Cd4 silencing in CD8 T cell progenitors, it is not required to maintain the silencing of Cd4 and other helper T lineage genes. The other runt domain containing protein, RUNX1, silences Cd4 in an earlier T cell progenitor, but this silencing is reversed whereas the gene silencing after RUNX3 expression is not reverse. Therefore, we hypothesized that RUNX3 and not RUNX1 recruits other factors that maintains the silencing of helper T lineage genes in CD8 T cells. To this end, we performed a proteomics screen of RUNX1 and RUNX3 to determine candidate silencing factors.
